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X-ray absorption and resonant inelastic X-ray scattering calculations with ligand field single cluster method on praseodymium nickel oxide

University of British Columbia

RNiO3 perovskites (R=rare earth) are one of the most interesting compounds in condensed matter physics presenting various unusual physical properties. The detailed electronic structure of these materials are very controversial at the present time. The charge transfer energy and the d-d Coulomb interaction are the two very important parameters which can explain their electronic behaviours nicely. However, predicting their values has been a challenge to the science society so far. X-ray Absorption Spectroscopy (XAS) and Resonant Inelastic Scattering (RIXS) are the two very useful techniques to probe the electronic structure of a solid state system in general and predict these two energies in particular. In this thesis Multiplet Ligand Field Cluster Calculation (MLFCC) is used to calculate these two spectra, then the charge transfer energy (Δ), the covalent hopping integral(pds), and the d-d Coulomb repulsion energy Udd are obtained by fitting the calculated spectra to the experiment. In this work, the calculated XAS results are compared with the experiment and the adjusted values are introduced as Δ=2.5eV , pds=-1.9eV, Udd=7.5eV and 10Dq=0.5 eV. The low spin to high spin transition is also studied and the critical charge transfer energies and covalent hopping integrals are calculated at which the abrupt transition happens. It is also found that in almost all low spin cases the d8L9 configuration has the largest contribution to the ground state. Since the best fit of XAS is not satisfactory and displays considerable differences with the experiment, the study is followed with the RIXS calculations. Finally, the calculated RIXS results for different polarizations are compared with the experiment.It results in a smaller Δ=0.8eV and a smaller absolute value of pds=-1.4eV at which the double peak structure in XAS L3 vanishes. This could be an evidence to the fact that XAS should not be interpreted in the conventional way and the Δ should not be fitted to keep the double peak which probably has another source than the multiplet structure.

Text

2013-10-25

Attribution-NonCommercial-ShareAlike 2.5 Canada

http://hdl.handle.net/2429/45392

Physics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-sa/2.5/ca/